1. Field of the Invention
The present invention pertains to the field of shielding structures for radiation procedure tables. In particular, the present invention pertains to adjustable X-ray shields for procedure tables and adjustable X-ray shielding systems using on-line radiation dosimetry.
2. Description of the Related Art
During certain procedures, for example, those involving the insertion of an intravascular catheter (procedures such as atherectomy, balloon angioplasty, stent placement and the like), patients are required to lay prone on an X-ray procedure table. The physician then inserts a guidewire or a catheter device through a small incision, often near the patient's groin, and advances the device through an artery to the target site.
To facilitate imaging of the intravascular device during use, the device may include a radio-opaque distal tip to allow the physician to guide the device under fluoroscopic observation to the desired site. During such procedures, the physician controls an X-ray tube, the source of the radiation used to visualize the target arterial site and the intravascular device, using a foot pedal. The X-ray tube is generally located underneath the table surface. The X-ray beam generated by the tube travels through the procedure table and the patient's body. The majority of the photons generated by the X-ray tube are scattered by the cells within the patient's body. A small portion of the generated X-ray beam, however, succeeds in traversing both the procedure table and the patient's body. A portion of the X-ray beam that traverses both the table and the patient's body reaches an image intensifier located above the patient. The image intensifier detects the photons, channels them through a photon multiplier and transfers the resulting intensified image to a display screen, which allows the physician to accurately guide the device.
Interventional procedures such as described above often take hours to complete, and may expose the physician and the patient to a significant amount of radiation that may, over time, pose serious health risks. To reduce the physician's exposure to scattered X-ray radiation, a number of protective measures have been implemented. The first of such protective measures is the use of X-ray shields. Several types of X-ray shields have been developed. Lenhart, for example, in U.S. Pat. No. 5,006,718, proposes a shield assembly wherein shielding material extends from the side of the table adjacent the physician to the floor. However, such shield, while affording an unobstructed view of the patient, does not appear to protect the physician from the large amount of radiation scattered from the patient's body and above the level of the table. Other solutions generally involve the use of horizontally disposed strips of radiation shielding material, such as disclosed by Collica et al. in U.S. Pat. No. 3,984,696, or the use of vertically disposed strips of radiation shielding material hung from a position above the patient's body, as disclosed in Lenhart, U.S. Pat. No. 4,581,538 and Stivender et al., U.S. Pat. No. 4,062,518. However, both of these approaches appear to share common disadvantages. The first of these is that the physician's view of the patient, and the patient's view of the physician is severely impaired by the strips of shielding material. The second of these disadvantages appears to be an incomplete shielding of scattered radiation, in that significant portions of the patient's body are directly exposed to the physician. During the interventional X-ray procedure, a significant amount of scatter from these exposed portions may reach the physician, with deleterious health consequences. Moreover, with such conventional X-ray shields, unintended gaps in coverage may occur due to improperly positioned or repositioned shields, unknowingly exposing the physician to greatly increased radiation levels until the gap is discovered, if ever. Indeed, the shield often must be re-positioned during the procedure when the orientation of the X-ray tube is changed to change the imaging angle. Failure to properly reposition the shield thereafter may result in gaps in the shielding material. As X-ray radiation cannot be seen, heard or felt, such gaps may remain undiscovered and may expose the physician and other personnel in the procedure room to needlessly increased radiation levels.
The second of such protective measures to protect the physician from unwanted scatter is the so-called lead apron. The lead apron is an article of clothing donned by the physician prior to a catheter procedure. The lead apron generally covers at least the neck including the thyroid, the torso, and the thighs. Leaded eyeglasses may also be worn. The apron is effective in significantly reducing the physician's instantaneous and cumulative exposure to X-ray radiation over time, at least with respect to the areas covered by the apron. In contrast, uncovered areas, such as the physician's hands, arms and lower legs, are protected, if at all, solely by the table's X-ray shield. Common lead aprons are equivalent to a lead barrier of about 0.25 to 0.5 millimeters in thickness. However, such protection, while effective, does not come without discomfort to the physician. Indeed, such lead aprons commonly weigh about fifteen to twenty pounds. As the physician may be required to bend over the patient for periods of time often measured in hours, a significant proportion of the weight of the lead apron may be borne by the physician's lower back, shoulder and neck area. Supporting such weight can, over time, cause intense lower back, neck and shoulder pain, particularly for those suffering from already weakened backs.
What is needed, therefore, is an X-ray shield for an X-ray procedure table that more effectively protects the physician from X-ray scatter. What is also needed is an X-ray procedure shield for an X-ray procedure table that is highly effective in attenuating X-ray scatter while affording the physician a relatively unobstructed view of the patient during the X-ray procedure. What is also needed is an X-ray shield that is sufficiently effective in attenuating radiation to allow the physician to wear a lighter apron (e.g. one having a lower lead equivalency rating) or to allow the physician to safely forego wearing a lead apron or other uncomfortable protective gear altogether. Also needed are means for insuring, at all times, the proper positioning of the X-ray shield to achieve the greatest possible attenuation of radiation.